Shielded electrical inductive apparatus



0 United States Patent 1111 3,546,358

[72] Inventor meter y u [56] References Cited Nurnberg, Germany UNITEDSTATES PATENTS [21] A pp 715,620 1,697,142 1/1929 Roller l74/35(.4)UXliiled d $32 3 3 1,942,575 1/1934 Shapiro 174/35(.3)x

meme FOREIGN PATENTS Aktlengesel [73] :Z'Ig 315,372 4/1930 Great Britain336/84 390,500 4/1933 Great Britain... 336/84 a corporation of Germany[32] Priority April 7, 1967 632,125 11/1949 Great Br1ta1n 336/84 [33]Germany Primary Examiner-Darrell L. Clay [31 1 No. 5109230 Attorneys-A.T. Stratton, F. E. Browder and Donald R.

Lackey ABSTRACT: Electrical inductive apparatus having a flux producingcomponent disposed within a casing formed of a metallic, magneticmaterial, and shielding means disposed [54] igi i f g g INDUCTWE betweenthe flux producing component and the casing. The 6 cm 11 D h m shieldingmeans is formed of at least one layer of a woven 8 fabric, with thefabric strands which run parallel with one [52] [1.8. CI. 174/35,another in a first direction being formed of metallic wire. The 336/84fabric strands which run parallel with one another in a second [51]lnt.Cl. ..H0lf15/04, direction, and which are woven with the metallicstrands of l-l05k 9/00 the first direction, are formed either of anelectrical insulating olsell'ch material, or of metallic wires which areelectrically insulated from the metallic wires of the first direction.

PATENTED DEC-81976 SHEET 1 OF 2 J l/ J l J l4 FIGI FIG. 20.

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lllllllll lllllll I llllllll SHEET 2 OF 2 o, o J l llllllll l llllllll lI lllllll l I llllllJ 1 SHIELDED ELECTRICAL INDUCTIVE APPARATUSBACKGROUNDOF THE INVENTION 1. Field of the Invention The inventionrelates in general to means for shielding stray magnetic fieldsassociated with electrical inductive apparatus such as transformers androtating electrical machines.

2. Description of the Prior Art Stray fluxes produce appreciableeddy-current losses in massive component members and walls of largesurface area such as occur, for example, in electrical machines. Theselosses can be reduced by employing different types of wellknownstray-flux shields. Of course, observable losses also occur in thescreens themselves If, for example, copper or aluminum shields areemployed, they must have an appreciable thickness in order to satisfythe shielding requirements. By employing magnetically permeablesheet-material screens, such as sheet iron, the formation of sheet fromthin layers, and hence subdividing the said sheet into mutually,electrically insulated layers-produces a reduction in the longitudinallosses caused by the stray fluxes traversing the sheet surface. Theappreciable transverse losses which arise from the entry and exit of thestray flux into and out of the plane of the sheet can only be reduced bysubdividing the sheet material into individual electrically insulatedstrips. This possibility can only be employed to a limited extentbecause sheet material can only be slit and machined to breadths ofabout 1 cm. in an economical manner.

SUMMARY OF THE INVENTION Briefly, the disadvantages of prior artshielding are obviated, according to the teachings of the invention, byemploying multilayered woven wire fabric for shielding purposes.

The entry and exit losses become vanishingly small using surfaces madefrom parallel'wires, for in this case similar sheet-surfaces are presentwhich are subdivide into the finest insulated strips. In addition, thelosses in the longitudinal direction of the plane surface can be reducedin this manner, mainly because wire can be produced which is muchthinner than sheet. Thus, both the longitudinal and transverse lossesbecome smaller, the thinner the wire employed.

The technological advance provided by the invention when compared withthe the prior art procedure of subdividing sheet into the thinnest ofstrips lies, in the main, in the use of less costly products, namelywoven wire cloth, whose commercially available forms can be made to suitthe proposed .usage in an optimum manner.

As a woven wire fabric, it is possible to employ woven iron in which atleast one direction of the wire fibers is electrically insulated, or afabric can be used in which the fibers in one direction consist of aninsulating material, while the other consists of iron. Thecharacteristic form of the weave ensures good and uniform electricalinsulation of the iron wires.

The insulating fibers can be made of plastics, such as nylon, forexample. Exceptionally good space-filling can be obtained when the ironwires are packed together as closely as possible. This situation can beobtained if, for example, the thickness of the insulating fibers isappreciably smaller than that of the iron wires. Good space utilizationalso signifies that the total space employed by the screening device isfilled to the greatest possible extent with magnetically effective iron.The better the space-usage, the less space is occupied by the screeningdevice. This can be of very great significance when it is required toproduce the most compact form of electrical machines.

Iron wire-synthetic fiber woven fabrics, such as those already employedfor other purposes, will serve to produce compound-packaging of severallayers of parallel wires. In this regard, the warp may consist of ironwire and the woof, for example, of nylon threads, or the reverse. Thefabric faces can easily be finished in many ways and joined togetherwith resins to form multilayer sheets. This compound sheet materialshould display great improvements in fatigue strength by com- IIIparison with glued (cemented) sheets because there are no outstandingplanes of preferred strength and an altogether more uniform material isproduced.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of theinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIG. 1 provides a schematic representation of a magnetically permeableshield into which penetrates a stray flux (stray magnetic field);

FIGS. 2a and b show schematically the magnetic flux and the eddy-currentflow pattern in a round iron wire;

FIGS. 30 and b show schematically the transverse magnetic circulation inparallel iron wires;

FIG. 4 provides a schematic representation of a commercially availablewoven wire fabric;

FIGS. 5a and b show schematically woven iron fabrics having improvedspace-filling in accordance with the invention;

FIG. 6 shows in graphicalform the ratio of the eddy-current losses inwire to the the losses in sheet material or to the losses in sheetmaterial subdivided into strips during longitudinal magnetic circulationas a function of the wire diameter of a woven wire fabric plate;

FIG. 7 shows in graphical form the ratio of the eddy-current losses inwire to the losses in sheet material, or to the losses in sheet materialsubdivided into strips, during transverse magnetic circulation, as afunction of the wire diameter of a woven wire fabric plate; and

FIG. 8 is a plan view of electrical inductive apparatus, shieldedaccording to the teachings of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, andFIG. 1 in particular, there is shown a schematic representation of thegeneral case of a prior art magnetically permeable shielding plate intowhich is passing a stray flux (side view). The flux forced into theshielding plate is transmitted longitudinally and then emerges again.Shielding plate 11 is subdivided into several layers 12. The path takenby the stray flux I is shown by the arrows 13. The regions of transversemagnetic circulation (flow) are denoted by 14, while-15 denotes thoseregions in the shielding plate where the magnetic circulation islongitudinal.

FIGS. 20 and 2b show in a schematic manner the paths taken by themagnetic flux and the eddy-current in an iron wire of circular crosssection. In FIG. 2a, the magnetic flux 21 in the longitudinal directionof an iron wire 23 is indicated by the arrow 22. In FIG. 2b, thecircular-shaped eddy-current produced around the longitudinal axis ofthe iron wire by the magnetic flux are denoted by 24.

The transverse magnetic circulation in parallel iron wires in differentrelative positions is shown schematically in FIGS. 3a and 3b. The wiresare denoted by 31 and the lines of magnetic flux by 32. I

FIG. 4 shows in cross section a schematic representation of acommercially available woven wire fabric with insulating fibers. Theiron wires are denoted by 41 and the insulating fibers by 42.

FIGS. 5a and 5b show woven wire fabrics which, in accordance with theinvention, are suitable for improving the use of space on account oftheir design. Thus, for example, FIG. 5a shows a woven wire fabric witha ratio of wire thickness of wire 51 to fiber thickness of insulatingfiber 52 of 4:1. FIG. 5b shows that wires 53 can be satisfactorilyaligned by weaving in the form of flat wire and held in place, the saidwires being converted to the finest of strips by rolling, such a degreeof fineness being unobtainable by the slitting of sheet material. Suchflat wires, made from thicker material, can produce the same reductionin the longitudinal losses as correspondingly thinner wire of circularsection, whereby the otherwise most greatly weakened and vanishinglysmall transverse losses are increased somewhat. An additional advantageis that of a higher space-filling. This is because of flat wire,

considered in cross section, corresponds to a series of parallel finewires which are not insulated from each other. In this case, again, theinsulating fibers are identified by the number 54.

It is possible to obtain an increase in the space-utilization of thedevice made in accordance. with the invention by employing other methodssuch as, for example, by different forms of weaving. The wire warp canbe made closer. In such a case, the woof must consist of very fineinsulating threads each consisting of several fibers, if necessary, toretain their strength, instead of the woof consisting, in customaryfashion, of a single or two-ply fiber which corresponds closely inthickness to that of the wire. In addition, by heating of multiplelayers of woven-wire fabric until softening of the insulating fibersconsisting of, for example, thermoplastic synthetic fibers, and bysimultaneous or subsequent pressing, it is possible to reduce thedistance between the wire-planes (layers) set by the synthetic fibers.The layers can thus be baked together. By this means, it is possible toimprove the strength of the material because the bonding-system is nowvirtually free from layerorientation. The combining of the strips ofwoven material to form a composite sheet can be effected in the usualmanner as in the production of conventional plied materials such as, forexample, resin bonded fabrics, This can be further extended or improvedby the interposition of layers of thermoplastic films or thermoplasticfabrics or thermoplastic flakes or thermoplastic mats or by thescattering of thermo or Duroplastic powder or thermo or Duroplasticshavings on the surfaces and finally pressing with the application ofheat, or by the use of glues or other bonding materials, such as, forexample, by soaking with a casting resin. During the the process ofpressing the sheets together, it is possible to ensure a minimumresidual separation by means of woven-in or inserted insulating fibersof higher thermal resistance or by electrically insulating the wires, asconventionally provided in the case of sheet material. The materialsconsisting of layers of woven-wire fabric can also be bonded together bymeans of sprayed-on liquified thermoplastics.

If the strips of woven fabric are placed on top of each other with thenap running in the same direction and then bonded into a multiply sheet,one obtains two preferred magnetic directions for a materialincorporating iron wire in both the warp and the woof, whereas, only onepreferred direction of magnetization is obtained in the wire-directionfor a material having an iron wire warp and an insulating fiber woof.Thus a preferred direction can be provided for cases where the strayflux is in a known, constant direction. At the same time, the bestmagnetic use is made of the iron cross section in the shielding device.

By superimposing layers with their naps aligned in different directions,it becomes possible to provide several magnetically preferreddirections, corresponding to the wire directionsas would be required forwandering stray fluxes or fluxes of different direction.

The preferred magnetic directions do not have to be rectilinear. Rather,they can follow the most advantageous curved paths consistent with theprevailing conditions becauseespecially prior to the bonding themultilayered composite-the woven wire fabric can just as easily bewarped in the plane of the sheet as bent at right-angles to it,

By adding iron powder to the above above-mentioned bonding media, it ispossible to attain an improvement in the mag netic conductionperpendicular to the direction of the wires, from layer to layer or fromone wire direction to another.

The above-described methods of bonding can also be employed in anyarbitrary combination.

FIG. 6 gives a graphical representation of the ratio of the eddy-currentlosses P,, in the wire to the losses P,, which occur either in sheetmaterial or sheet material which has been subdivided into strips, theratio being for longitudinal magnetic flux and drawn as a function ofthe wire-diameter D of a wire in a woven wire fabric plate. Thewire-diameter D in mm. is plotted as abscissa and the ratio P, /P,, asordinate. The numerals associated witheach line in the graphs refer tothe parameter, that is, to the thickness in mm. of the sheet material orto the strips ofsheet material. I

From the graphs shown in FIG. 6 it is easy to read off the reduction inthe losses by the use of woven wire fabrics with longitudinal magneticflux. Thus, the longitudinal losses are reduced by about l percent, forexample, by employing woven wire fabric with a wire diameter of 0.5 mmvby comparison with sheet material having a thickness of5 mm. With thesame thickness of wire and sheet, the losses are reduced by about 40percent.

FIG. 7 provides a graphical representation ofthe ratio of theeddy-current losses P,, in the wire to the losses P in sheet or in sheetsubdivided into strips, the ratio being for transverse magnetic flux andshown as a function of the diameter D of a wire in a woven wire plate.Here, again, the wire diameter is taken in mm. as the abscissa while theordinate is plotted with the ratio P /P The reference numbers on thecurves again refer to the parameter which in this case can be thebreadth in cm. of the sheet material or of the strips.

As far as the transverse losses are concerned, entire sheets andlaminated stacks of sheet are equivalent. A significant reduction couldbe obtained in the transverse losses by subdividing the sheet-layersinto strips. From the graphs shown in FIG. 7, one can see the advantageto be gained by employing woven wire fabric instead of strips of sheetmaterial for shielding. For example, with a strip width of 10 mm. and awire diameter of0.5 mm. a loss-reduction P,1/P,, of about l percent isobtained. In the comparisons made in accordance with FIGS. 6 and 7,equal volumes and equal average inductions for sheet and wire are takenas a basis, as well as average property values for single-ply dynamo andsteel sheet.

FIG. 8 is a plan view of electrical inductive apparatus with its coverremoved, such as a transformer or reactor, illustrating how theteachings of the invention may be applied. Electrical inductiveapparatus 80 includes a flux producing component 82, which in thisinstance is illustrated as being a core-winding assembly of a polyphasetransformer or reactor ofthe core-form type, having electrical windingassemblies 84, 86, and 88 disposed in inductive relation with a magneticcore 90. The core-winding assembly 82 is disposed within a tank orcasing 92 which is formed of a metallic, magnetic material, such assteel. In order to shield the tank walls from stray magnetic flux, andthus prevent objectionable energy losses and excessive heating of thetank walls, shielding means 94, 96, 98 and 100 are disposed between thecore-winding assembly 82 and the sidewalls of the casing 92. Similarshielding means may be disposed to shield the bottom and cover of thecasing, if necessary.

Shielding means 94, 96, 98'and 100 are formed according to the teachingsof the invention, each having one or more layers of plies of a wovenfabric, in which metallic wire is used to form the strands which runparallel with one another in a first direction. The strands which arewoven with the strands of the first direction, are either formed of anelectrical insulating material, or of metallic wires which areelectricallyinsulated from the metallic wires of the first direction.

As illustrated in FIG. 8, the shielding means may be secured in thedesired location relative to the inside of the casing by suitableanchors 102 which are secured to the casing and project outwardlytherefrom to engage suitable openings in the shielding means. Theshielding means may be a plurality of sheets, as illustrated, or onecontinuous sheet may be used, depending upon the size of the apparatusto be shielded, and the economically practical maximum dimensions of thesheetlike shielding means.

While apparatus 80 shown in FIG. 8 is illustrated as being a polyphasetransformer or reactor of the core-form type, it is to be understoodthat the teachings of the invention may be beneficially applied tosingle-phase transformers and reactors of the core and shellform types,and to polyphase transformers and reactors of the shell-form type, aswell as generally to any encased flux producing component whose casingis to be shielded from stray magnetic flux.

Although the invention, has been described using magnetic wires, such asiron or steel, for the strands of the woven fabrics, which shield thecasing of a flux producing component by shunting the flux away'from thecasing, it is within the scope of the invention to use nonmagneticmetallic wires, such as aluminum or copper, and shield the casing bysetting up a counter flux which opposes the flux from the flux producingcomponent, and, therefore, reduces the total amount of flux reaching'thecasing. Or, a combination of magnetic and nonmagnetic metallic wires maybe used.

lclaim:

1. Electrical inductive apparatus comprising:

a magnetic flux producing component; l

a metallic casing;

said flux producing component being disposed within said casing; 1

and shielding means disposed between said flux producing component andat least a predetermined portion of said metallic casing; and

said shielding means consisting of a plurality of layers of a wovenfabric, said woven fabric having a plurality of metallic strands runningin a first direction, woven with a plurality of thermoplastic insulatingstrands running in a second direction, the material of saidthermoplastic insulating strands bonding the plurality of layers ofwoven fabric together.

2. The electrical inductive apparatus of claim 1 wherein the metallicstrands are magnetic.

3. The electrical inductive apparatus of claim 1 wherein the thicknessof the metallic strands is greater than the thickness of the insulatingstrands.

4. The electrical inductive apparatus of claim 1 wherein the metallicstrands are substantially flat, having first and second dimensionswherein the first dimension is substantially greater than the seconddimension.

5. The electrical inductive apparatus of claim 1 wherein the first andsecond directions of the strands run in the same directions in each ofthe layers of the woven fabric, with respect to the shielding means.

6. The electrical inductive apparatus of claim I wherein the first andsecond directions of the strands, in at least two of the plurality oflayers of woven fabric, run in different directions, relative to theshielding means.

